Method and device for displaying at least two images within one combined picture

ABSTRACT

The invention relates to a method and a device [to display]* at least two overlapping images (M, S) within one combined picture (G), wherein a third video signal (VMS) is generated from a first video signal (VM) containing the video information for a first image (M) displayed in a first active region (A 1 ), and from a second video signal (VS) containing the video information for a second image (S) displayed in a second active region (A 2 ), the third video signal containing video information for an image displayed within an overlap region (A 12 ) of the first and second regions (A 1,  A 2 ).

[0001] The invention relates to a method of displaying an image from afirst video channel and an image from a second video channel within onecombined picture, and to a device for implementing this method.

[0002] In order to display an image from a first video channel and animage from a second video channel within one combined picture, a knownapproach is to feed a first video signal and a second video signal to amultiplexer, wherein the first video signal contains video informationfor a first image to be displayed in a first active region of thecombined picture, and the second video signal contains video informationfor a second image to be displayed in a second active region of thecombined picture. In the known method, the multiplexer generates anoutput video signal from the first and second video signals which may beutilized to display the combined picture by means of a conventionaldisplay device such as a monitor.

[0003] The combined picture is built up line-by-line, that is, the videoinformation for adjacent pixels within the combined picture is presentin the output signal in temporally sequential form. Similarly, the firstand second video signals contain video information for adjacent pixelsin temporally sequential form. For each pixel whose video information iscontained in the output signal, the multiplexer decides whether thepixel lies within the first or second active regions of the combinedpicture, or outside of these active regions. If the pixel lies withinthe first active region, the multiplexer transmits the first videosignal, or the video information from this video signal, to the outputto generate the output signal. If the pixel lies within the secondactive region, the multiplexer transmits the second video signal to theoutput, and if the pixel lies outside the first and second activeregions the multiplexer transmits a video signal for a background imageto the output. The sequential values of the output signal which containsthe line-by-line information for the combined picture are thus obtainedfor the background image from the first or second video signalsdepending on the position of a given pixel within the combined picture.

[0004] To enable the decision to be made as to whether a given pixellies within or outside of the first or second active regions, themultiplexer is fed control signals which contain information on theposition and dimensions of the active regions.

[0005] If the first and second active regions overlap, a priority signalis referenced to decide whether to take the video information for agiven pixel of the overlap region from the first or second videosignals, the priority signal determining which of the video signals touse to display the pixels of the overlap region, that is, which of thetwo images must be in the foreground while the other of the two imagesis partially or completely covered. Given two images to be displayed,the priority signal may assume two different values such that if thereis a change in the priority signal, the image previously displayed inthe background may now move to the foreground.

[0006] The known method permits only the display of the videoinformation from one of the video signals in the overlap region.

[0007] The goal of the invention is to provide a method for displaying afirst and a second image within a combined picture which allows for thedisplay of video information from the first and second video signalswithin the overlap region, and in which specifically cross-fading fromthe first to the second image within the overlap region is possible whenthe image to be displayed in the foreground changes.

[0008] This goal is achieved by a method according to claim 1. A devicefor implementing the method according to the invention is the subject ofclaim 8.

[0009] Advantageous embodiments of the invention are described in thesubclaims.

[0010] The method according to the invention for displaying a first andsecond image which at least partially overlap within one combinedpicture provides a first video signal for displaying the first imagewithin a first active region of the combined picture, and a second videosignal for displaying the second image in a second active region of thecombined picture. According to the invention, a third video signal isgenerated from the first video signal and the second video signal, andan output signal for displaying the combined picture is generated fromthe first, second, and third video signals, the video information fromthe third video signal being used only to display the pixels of theoverlap region.

[0011] The information on the position and dimensions of the firstactive region is preferably contained in a first control signal, theinformation on the position and dimensions of the second active regionis preferably contained in a second control signal, and the informationon the position and dimensions of the overlap region is preferablycontained in a third control signal, these control signals [beingemployed]* to decide whether a given set of video information from thefirst, second or third video signals is mapped to the output signal. Thethird video signal has the highest priority here, that is, videoinformation for pixels of the overlap region are always obtained fromthe third video signal.

[0012] Various approaches are provided to generate the third videosignal from the first and second video signals, which approaches may beemployed either independently of each other or sequentially.

[0013] According to a first embodiment, the first and second videosignals are added together. Pixels are thus produced within the overlapregion, the video information of which results from a superposition ofthe video information from the first image and the second image.

[0014] According to a second embodiment, before addition of the firstand second video signals, the first video signal is weighted by a firstweighting factor and the second video signal is weighted by a secondweighting factor. The extreme case in which one of the weighting factorsis one and the other weighting factor is zero corresponds to the case inwhich the video information for the pixels of the overlap region areobtained only from one video signal, that is, the video signal weightedby the weighting factor one. This situation corresponds to displayingthe image for which the video signal is weighted by the weighting factorone in the foreground.

[0015] The weighting factors may under go a temporal variation, and/orthey may undergo a spatial variation, that is, a variation dependent onthe position of the display pixel within the overlap region. A temporalor spatial variation of the weighting factor enables a temporal orspatial cross-fading of the display from the first image to the secondimage in the overlap region.

[0016] During temporal variation, the weighting factor of the one videosignal is initially one and then changes over time to zero, while theweighting factor of the other video signal changes from zero to one. Thetime period in which the transition occurs is selected so that it isgreater than the time period within which the video information for adisplay image or half-image is transmitted, the time period preferablyamounting to at least a few seconds such that a slow continuoustransition for the human eye occurs in the overlap region from thedisplay of the video information of the one video signal to the displayof the video information of the other video signal.

[0017] According to one embodiment of the invention, the overlap regionis subdivided into a grid such as a checkerboard pattern, and the videoinformation from the first and the second video signals is alternatelydisplayed in the individual fields of this grid. This action is achievedby weighting factors which assume the value one or zero in the overlapregion depending on the position of the display pixel. The weightingfactors may additionally undergo a temporal variation which allows forcross-fading from the display of an image in the overlap region via thedisplay of the “checkerboard pattern” to the display of the videoinformation of the other image in the overlap region.

[0018] Any other temporal variations or variations dependent on theposition of the pixels are conceivable to produce the display of thevideo information in the overlap region. It should be pointed out that aposition-dependent variation of the weighting factors also represents atemporal variation since the video information for the individual pixelsis present in the video signals in a temporally sequential form. Thesevariations occur, however, within a temporally defined frame.“Position-dependent variation of the weighting factors” below alwayssignifies a temporal variation within a time frame permanently definedby the image structure, while “temporal variation of the weightingfactors” signifies a variation over multiple individual images of theimage sequence to be displayed.

[0019] In addition, the object of the invention is a device forproviding an output signal which is used to display at least a firstimage from a first video signal and a second image from a second videosignal within one combined picture, where the two images overlap atleast partially. The device has a first input for feeding a first videosignal to display the first image within a first active region of thecombined picture, and a second input for feeding a second video signalto display a second image within a second active region of the combinedpicture.

[0020] The device has a logic circuit with at least one adder to add thefirst and second video signals in order to form a third video signal,and a multiplexing device to which the first, second, and third videosignals are fed, and which multiplexing device provides an output signalfor the combined picture.

[0021] In addition, a first control signal containing information on theposition and the dimensions of the first active region, and a secondcontrol signal containing information on the position and dimensions ofthe second active region may be fed to said device, these controlsignals being capable of being fed either to separate control inputs ofthe device or together with the video signals containing the videoinformation. The assignment of the first, second, and third videosignals to the output signal in the multiplexing device is effected as afunction of the control signals, the third video signal generated fromthe first and second video signals being employed to display the pixelsof the overlap region.

[0022] According to one embodiment of the invention, a first multiplierfor multiplying the first video signal by a first weighting factor, anda second multiplier for multiplying a second video signal by a secondweighting factor are connected in series ahead of the adder.

[0023] The following discussion explains the invention in more detailbased on exemplary embodiments and the figures.

[0024]FIG. 1 is a schematic view of a combined picture which contains afirst image in a first active region and a second image in a secondactive region, wherein the images partially overlap.

[0025]FIG. 2 shows a first embodiment of a device according to theinvention for providing an output signal which is suitable fordisplaying the combined picture.

[0026]FIG. 3 is a characteristic over time of the control signalscontaining information on the position and the dimensions of the activeregions.

[0027]FIG. 4 shows a device according to the invention based on anotherembodiment in which the first and second video signals are weightedbefore generation of the third video signal.

[0028]FIG. 5 is a schematic view of a combined picture in which thefirst and second video signals during generation of the third videosignal are uniformly weighted.

[0029]FIGS. 6 through 8 are schematic views of various combined picturesafter weighting of the first and second video signals as a function ofthe position of the given pixel in the overlap region.

[0030]FIG. 9 is a sequence of images illustrating weighting factorsvarying over time to achieve a temporal cross-fading effect.

[0031]FIG. 10 is a schematic view of another combined picture in whichthe images in the active regions are each surrounded by a frame.

[0032]FIG. 11 shows a device according to the invention based on anotherembodiment for generating a combined picture in FIG. 10.

[0033] Unless otherwise indicated, the same reference symbols in thefigures designate components of the same significance.

[0034]FIG. 1 is a schematic illustration of a combined picture whichhas, within a displayable screen region G, a first image M in a firstactive region A1 and a second image S in a second active region A2, thefirst and second active regions A1, A2 having an overlap region A12 inwhich the first and second images M, S overlap. A background image B isdisplayed in the area outside the first and second active regions A1,A2.

[0035]FIG. 2 is a schematic view of a first embodiment of a device 110according to the invention for generating an image signal OUT whichcontains the video information of a combined picture of the type shownin FIG. 1 with at least two superimposed combined pictures M, S, andwhich may be employed in a conventional video display device to displaythe combined picture.

[0036] A first video signal VM containing the video information of thefirst image M displayed in the first active region A1 is fed to device110, while a second video signal VS containing the video information ofthe second image S displayed in the second active region A2 is fed tosaid device.

[0037] The image displayed from the output signal OUT is built upline-by-line, that is, the video information for adjacent pixels presentin one line, and the video information for the pixels in lines lyingbelow each other are contained in temporally sequential form in theoutput signal OUT. Similarly, first video signal VM and second videosignal VS contain the video information in line-by-line temporallysequential form to display the first image M in first active region A1,or to display the second image S in second active region A2.

[0038] A first control signal MS is assigned to first video signal VM,and a second control signal SS is assigned to second video signal VS,the control signals determining the position and dimensions of activeregions A1, A2 within the combined picture. FIG. 3 is a schematic viewof the characteristic over time of an example of such control signalsMS, SS which are periodic at the frequency of the displayed combinedpicture, usually 50 Hz.

[0039] Time period T in FIG. 3 designates the time period within whichthe video information for the line-by-line build-up of the combinedpicture is transmitted. Tz designates the time period within which thevideo information of one line is transmitted. Active regions A1, A2 inwhich the video information from the first or second video signals VM,VS are displayed each represent only a segment of the displayable imageregion G. The time periods at which control signals MS, SS in FIG. 3assume an upper signal level are the time periods at which the videoinformation for the pixels of active regions A1, A2 are transmittedwithin total time T. The temporal portion of the segments which assumean upper signal level at time period Tz corresponds to the ratio of thewidth of combined picture G to the width of the respective activeregions A1 or A2. The number of segments MS, VS for which the controlsignals assume an upper signal level corresponds per period to thenumber of lines from which the respective active region is built up.

[0040] The first and second video signals VM, VS and their associatedcontrol signals are fed to the multiplexing device MUX which combinesfirst and second video signals VM, VS to form the output signal OUT.Control signals MS, SS, MSS may be fed to the multiplexing device MUXseparately from the video signals VM, VS containing the videoinformation, or control signals MS, SS may be fed to multiplexing deviceMUX together with video signals VM, VS, that is, control signals MS, SSmay be modulated upon video signals VM,VS, a separation into videosignals VM, VS and control signals MS, SS then being effected inmultiplexing device MUX. In the embodiment of FIG. 2, video signals VM,VS and their associated control signals MS, SS are fed to multiplexingdevice MUX separately.

[0041] According to the invention, a third video signal VMS is generatedfrom first video signal VM and second video signal VS. In the embodimentof FIG. 2, an adder is provided for this purpose which adds the firstand second video signals VM, VS. This third video signal VMS containsthe video information of image MS in overlap region A12. A third controlsignal MSS is assigned to third video signal VMS; an example of thiscontrol signal is shown in FIG. 3c which is produced by an AND relationof first and second controls signals MS, SS. Third video signal VMS andits associated control signal MSS are also fed to multiplexing deviceMUX.

[0042] In addition, a fourth video signal VB to display the backgroundimage B is fed to device 110 and multiplexing device MUX of FIG. 2.

[0043] Output signal OUT contains the video information in temporallysequential form for the adjacent pixels in the line-by-line-generatedcombined picture. Based on control signals MS, SS, MSS, multiplexingdevice MUX decides for each pixel of the combined picture generated fromoutput signal OUT whether the pixel lies within first active region A1,within second active region A2, within overlap region A12 of first andsecond active regions A1, A2, or outside of these regions. If thedisplay pixel lies within first active region A1 but not in overlapregion A12, the associated video information from first video signal VMis accepted for output signal OUT; if the display pixel lies withinsecond active region A2 but not within overlap region A12, theassociated video information from second video signal VS is accepted foroutput signal OUT; and if the display pixel lies within overlap regionA12, the associated video information from third video signal VMS isaccepted for output signal OUT. For pixels outside the first and secondactive regions A1, A2, the video information from fourth video signal VBis accepted for output signal OUT. In contrast to known methods, aseparate video signal VMS containing the video information for displayin overlap region A12 is assigned to the overlap region in the methodaccording to the invention. In the device used in FIG. 2, the videoinformation for the pixels of overlap region A12 is produced from asuperposition of the video information from first video signal VM andsecond video signal VS. The third video signal has the highest priorityhere, that is, it is always the video information from third videosignal VMS that is used to display the pixels in overlap region A12.

[0044]FIG. 4 shows another embodiment of a device 120 according to theinvention employed to generate an output signal OUT from first andsecond video signals VM, VS. In this embodiment, the following areconnected in series before adder ADD: a first multiplexer MUL1 whichmultiplies first video signal VM by a first weighting factor m1, and asecond multiplexer MUL2 which multiplies second video signal VS by asecond weighting factor m2.

[0045] Weighting factors m1, m2 may be fixed values or may varytemporally and/or spatially as explained below.

[0046]FIG. 5 shows a combined picture generated by a system in FIG. 4which for purposes of illustration has a black first image M in firstactive region A1, and a second white image S in second active region A2.The weighting factors m1, m2 for displaying the image in FIG. 5 are 0, 5respectively—with the result that the video information for first imageM and second image S are superposed in overlap region A12 to form a grayimage MS.

[0047]FIG. 6a illustrates another combined picture in which weightingfactors m1, m2 undergo a spatial variation, that is, they are dependenton the position of the display pixel within overlap region A12.Weighting factors m1, m2 have been selected here so that theyalternately assume the value one or zero for successive pixels, or anumber of successive pixels, from overlap region A12, thereby creating acheckerboard pattern within overlap region A12, the video informationfrom first video signal VM being displayed in those fields in whichfirst weighting factor m1 is one, and the video information from secondvideo signal VS being displayed in those fields in which secondweighting factor m2 is one.

[0048]FIG. 6b is the characteristic over time for first and secondweighting factors m1, m2 for the image displayed in FIG. 6a. Signal MSSdesignates the control signal for the third video signal, where thetemporal ranges in which control signal MSS assumes an upper level markthose temporal ranges in which the video information of each line of theoverlap region is transmitted. As the characteristics over time forweighting factors m1, m2 indicate, the temporal segments in which thefirst and second weighting factors m1, m2 each assume the value one orzero, alternate.

[0049]FIG. 7 shows another combined picture in which first and secondvideo signals VM, VS are added to generate the third video signal VMS,and are weighted before this addition. In this embodiment, the value forweighting factors m1, m2 is similarly dependent on the position of thedisplay pixel in overlap region A12. The relationship applicable here isthe following: first weighting factor m1 increases relative to secondweighting factor m2 the further the pixel lies within the upper leftcorner of overlap region A12, while second weighting factor m2 increasesrelative to first weighting factor m1 the further the display pixel lieswithin the lower right comer of overlap region A12.

[0050]FIG. 8 shows another embodiment in which overlap region A12 issubdivided, as in the embodiment of FIG. 6, into a grid where weightingfactors m1, m2 vary as a function of the position of the grid regionswithin overlap region A12.

[0051] In another embodiment, there is an additional feature beyondvarying the weighting factors as a function of the position of thedisplay pixel in overlap region A12: here the weighting factors varyover time—specifically over a time period extending over the display ofmultiple successive individual images, as is illustrated by the imagesequence in FIG. 9. Initially, first weighting factor m1 is one, causingthe video information of the first image M to be displayed in overlapregion A12, while first image M is in the foreground. Starting from thefirst image M in the foreground for the combined picture shown at thetop, a cross-fading takes place to the second image S located in theforeground as indicated in the last combined picture shown at thebottom. In the example, the cross-fading occurs in a grid pattern inwhich initially second weighting factor m2 increases in every otherfield of the grid, while first weighting factor m1 decreases until thevideo information for second image S is reproduced in these fields.Subsequently, first weighting factor m1 is reduced in the remainingfields, while second weighting factor m2 is increased until the videoinformation from video signal VS, or the second image, is alsoreproduced in these fields.

[0052] The fundamental aspect of the method according to the inventionis that a third video signal VMS is generated from the first and secondvideo signals VM containing the video information of first image Mdisplayed in first active regions A1, A2, and from the second videosignal VS containing the video information of second image S displayedin the second active region—this third video signal being treated as athird video channel when generating the output signal OUT. The videoinformation from third video signal VMS here always remains in theforeground.

[0053]FIG. 10 shows another combined picture in which a first frame G isdisplayed around first image M, and a second frame F is displayed aroundsecond image S, where images M, S and frames G, F surrounding the imagespartially overlap.

[0054]FIG. 11 shows an embodiment of a device 130 according to theinvention for generating an output signal OUT to display the combinedpicture.

[0055] In addition to first and second video signals VM, VS, and videosignal VS for the background image B, a video signal VG for first frameG and a second video signal VF for second frame F are fed to device 130.First video signal VM and the video signal for first frame VG are fed toa first multiplexer MUX1 to generate third video signal VMS, the firstmultiplexer MUL1 being connected in series after the output ofmultiplexer MUX1. In addition, second video signal VS and the videosignal VF for second frame F are fed to a second multiplexer MUX2, thesecond multiplexer MUL2 being connected in series after the output ofmultiplexer MUX2. First multiplexer MUX1 transmits the video informationfrom first video signal VM, or from video signal VG for first frame G,to its output as a function of a control signal mux1, control signalmux1 containing the information as to whether the display pixel belongsto first active region A1 or to the region of first frame G. Similarly,second multiplexer MUX2 transmits the video information from secondvideo signal VS, or from video signal VF for first frame F, to itsoutput as a function of a control signal mux2, control signal mux2containing the information as to whether the display pixel belongs tosecond active region A2* or to the region of second frame F.

1. Method for displaying a first image (M) and a second image (S) whichat least partially overlap within one combined picture (G), said methodincluding the following features: Supply of a first video signal (VM) todisplay the first image (M) within a first active region (A1) of thecombined picture (G), the first video signal (VM) containing the videoinformation for adjacent pixels of the first image (M) in temporallysequential form; Supply of a second video signal (VS) to display thesecond image (S) within a second active area (A2) of the combinedpicture (G), the second video signal (VS) containing the videoinformation for adjacent pixels of the first image (S) in temporallysequential form; Generation of a third video signal (VMS) from the firstand second video signals (VM, VS) to display a third image (MS) in anoverlap region (A12) of the first and second active regions (A1, A2);Generation of an output signal (OUT) to display the combined picture (G)which contains the video information for adjacent pixels of the combinedimage (G) in temporally sequential form, wherein the video informationfrom the first video signal (VM) is assigned to the output signal (OUT)whenever an associated pixel of the combined picture (G) lies within thefirst active region (A1), wherein the video information from the secondvideo signal (VS) is assigned to the output signal whenever anassociated pixel of the combined picture (G) lies within the secondactive region (A2), and wherein the video information from the thirdvideo signal (VMS) is assigned to the output signal (OUT) whenever anassociated pixel of the combined picture (G) lies within the overlapregion (A12).
 2. Method according to claim 1, in which the first videosignal (VM) and the second video signal (VS) are added to generate thethird video signal (VMS).
 3. Method according to claim 2, in whichbefore addition the video signal (VM) is multiplied by a first weightingfactor (m1), and in which before addition the second video signal (VS)is multiplied by a second weighting factor (m2).
 4. Method according toclaim 3, in which values for the weighting factors (m1, m2) are afunction of the position of the associated pixel within the overlapregion (A12).
 5. Method according to claims 3 or 4, in which theweighting factors (m1, m2) vary over a time period which is greater thanthe time period within which the video information for the combinedpicture (G) is transmitted.
 6. Method according to claim 5, in whichover time one of the weighting factors changes from one to zero, whilethe other weighting factor changes from zero to one.
 7. Method accordingto claim 3, in which the weighting factors are equal.
 8. Device fordisplaying a first image (M) and a second image (S) which at leastpartially overlap within a combined picture (G), said device having thefollowing features: a first input to feed a first video signal (VM) todisplay the first image (M) within a first active region (A1) of thecombined picture (G), wherein the first video signal (VM) contains videoinformation for adjacent pixels of the first image (M) in temporallysequential form; a second input to feed a second video signal (VS) todisplay the second image (S) within a second active region (A2) of thecombined picture, wherein the second video signal (VS) contains videoinformation for adjacent pixels of the second image (S) in temporallysequential form; a logic circuit (MUL1, MUL2, ADD) to which the firstand second video signals (VM, VS) are fed to generate a third videosignal (VMS) from the first and second video signals (VM, VS) to displaya third image (MS) within an overlap region (A12) of the first andsecond active regions (A1, A2); a multiplexing device (MUX) to which thefirst, second, and third video signals (VM, VS, VMS) are fed and whichprovides an output signal (OUT) to display the combined picture (G),wherein the multiplexing device (MUX) assigns the video information fromthe first video signal (VM) to the output signal (OUT) whenever theassociated pixel of the combined picture (G) lies within the firstactive region (A1), wherein the multiplexing device (MUX) assigns thevideo information from the second video signal (VS) to the output signal(OUT) whenever the associated pixel of the combined picture (G) lieswithin the second active region (A2), and wherein the multiplexingdevice (MUX) assigns the video information from the third video signal(VMS) to the output signal (OUT) whenever the associated pixel of thecombined picture (G) lies within an overlap region (A12) of the firstand second active regions (A1, A2).
 9. Device according to claim 8, inwhich control signals (MS, SS, MSS) are fed to the multiplexing devicewhich contain information on the position of the first and second activeregions (A1, A2) and of the overlap region, and which are employed inthe multiplexing device (MUX) to assign the video information from thefirst, second, and third video signals (VM, VS, VMS) to the outputsignal (OUT).
 10. Device according to claims 9 or 10, in which the logiccircuit (ADD, MUL1, MUL2) has an adder (ADD) which adds the first andsecond video signals (VM, VS) to generate the third video signal (VMS).11. Device according to claim 10, in which the logic circuit (ADD, MUL1,MUL2) has a first multiplier which is connected in series before theadder (ADD) and which multiplies the first video signal (VM) by a firstweighting factor (m1), and in which the logic circuit (ADD, MUL1, MUL2)has a second multiplier (MUL2) which is connected in series before theadder (ADD) and which multiplies the second video signal (VS) by asecond weighting factor (m2).